1. Field of the Invention
The present invention relates to a dielectric ceramic composition and a ceramic electronic part using the same. More particularly, the present invention relates to a dielectric ceramic composition suitable as a raw material for a multilayer electronic device such as a laminated-type ceramic capacitor, resonator, filter, and so on, particularly electronic device for micro waves, and to a ceramic electronic part using the dielectric ceramic composition.
2. Description of the Related Art
Ceramic electronic parts such as a multilayer ceramic capacitor, resonator, filter, and the like are generally prepared in which an electrode material and a dielectric ceramic composition are multilayer in sequence in a given lamination structure and they are sintered by burning them integrally. The lamination structure can make ceramic electronic parts compact in size yet high in performance.
A representative example of ceramic electronic parts of a multilayer type may include a multilayer ceramic capacitor of a compact size and a high capacity, which can be prepared by forming a dielectric ceramic composition of a barium titanate system and an electrode material composed of Ni metal in a given lamination structure and sintering them by burning them integrally at high temperature.
Recent years, portable communications devices utilizing micro waves having more than a GHz band have been used widely so that great demands have been made to develop ceramic electronic parts for micro waves, which have higher performance.
Characteristics of ceramic electronic parts for micro waves, in a first respect, are likely to undergo influences to a great extent from dielectric characteristics of a dielectric ceramic composition which is used as a raw material for a dielectric layer of the ceramic electronic part. As a dielectric ceramic composition for use as a material for the dielectric layer of a ceramic electronic part for micro waves, there are known, for example, dielectric ceramic compositions of a BaO--TiO.sub.2 series, BaO--Nd.sub.2 O.sub.3 --TiO.sub.2 series, MgTiO.sub.2 --CaTiO.sub.2 series, and so on.
The characteristics of the ceramic electronic parts for micro waves are also influenced by the electrical conductivity of a metal which is used as a raw material for an inner electrode. In this respect, it is preferred to use a metal having a high electrical conductivity as a raw material for the inner electrode of a ceramic electronic part. Such a metal may include, for example, Ag, Cu, and so on.
The melting point of Ag is 960.degree. C. and the melting point of Cu is 1,083.degree. C., while the temperature of sintering the dielectric ceramic composition for use as the raw material for the dielectric layer of the ceramic electronic part for micro waves is higher than 1,200.degree. C., so that the sintering temperature is considerably higher than the melting point of the metal suitable for the raw material of the inner electrode for the ceramic electronic parts. It is therefore impossible to burn the dielectric layer integrally with the inner electrode for sintering so that the metal such as Ag, Cu and so on cannot be used as a raw material for the inner electrode, although it is suitable therefor.
In order to allow the such metal to be used as the raw material for the inner electrode of the ceramic electronic part for micro waves, it is required that the temperature for sintering the dielectric ceramic composition for use as the raw material for the dielectric layer of the ceramic electronic part be lowered below the melting point of the metal such as Ag, Cu or the like to be used as the raw material of the inner electrode, that is, as low as approximately 900.degree. C. to 1,050.degree. C.
Generally, it is known that the temperature for sintering a dielectric ceramic composition can be lowered by adding a glass component as a sintering aid in the dielectric ceramic composition. As described above, the sintering temperature of the dielectric ceramic composition is as considerably high as 1,200.degree. C. or more, so that it is required to add a considerably large amount of a glass component to the dielectric ceramic composition in order to lower the sintering temperature to the range of approximately 900.degree. C. to 1,050.degree. C.
The addition of the glass component to the dielectric ceramic composition in such a large quantity, however, will cause a decrease in dielectric characteristics inherent in the dielectric ceramic composition which is used as the raw material for the dielectric layer of the ceramic electronic part for micro wave, thereby failing to achieve dielectric characteristics to the level as required.
With the foregoing drawbacks of the conventional sintering conditions taken into account, extensive review and studies have been made to provide a dielectric ceramic composition for use in sintering at temperature lower than the melting point of a metal suitable as a raw material of the inner electrode and capable of being burned integrally with the such metal for sintering, and to provide a ceramic electronic part having a high dielectric performance, which is prepared from the such dielectric ceramic composition. It has now been found that a dielectric ceramic composition having a particular composition can be sintered at a temperature low enough to be burned integrally with the metal such as, for example, Ag, Cu or the like, which is highly electrically conductive and useful as the raw material for the inner electrode of the ceramic electronic part, and that the dielectric ceramic composition can demonstrate sufficiently high dielectric characteristics that the major phase thereof should originally produce. It is also found that a ceramic electronic part having highly dielectric characteristics can be prepared by forming its dielectric layer from the such dielectric ceramic composition. The present invention has been completed on the basis of these findings.